Sample cup assemblies for use in spectrochemical analysis are well known in the prior art and consist essentially of a cup-shaped cell having a closed bottom and an open top, an annular collar, and a snap-on ring. An example of a typical prior art cup is shown in U.S. Pat. No. 4,409,854 entitled SAMPLE CUP WITH EMPTYING MEANS FOR USE IN X-RAY SPECTROSCOPY issued on Oct. 18, 1983 to Michael C. Solazzi an assigned to the assignee herein Chemplex Industries Inc. As can be seen, the collar and the snap-on ring serve to secure a sheet of plastic material such as MYLAR, the trademark for a polyester film sold by E.I. dupont de Nemours and Co., to cover the open top of the cell when the cell is filled with a specimen to be analyzed. The surface of the sheet of plastic is commonly defined as the sample plane.
The ability to statistically reproduce the distance from the sample plane to the excitation source is of utmost importance for exacting X-ray spectrochemical analysis. Deviations which may occur in this distance from one sample presentation to another will be reflected in the degree of analytical accuracy. This is because any variations in this distance operates to alter the intensity of the characteristic radiation of the specimen and the intensity of the radiation impinging upon the sample from the excitation source. Several factors have been discovered that predominately control the sample plane to excitation source distance. These factors include the geometry of the instrumentation optics, the type of sample substance, positioning of the specimen in the instrument sample chamber, heat generation from the excitation process, and pressure differentials attributed to operating in an evacuated or positive pressure condition and sample out-gasing. Any one of these factors or any combination thereof will effect the analytical data and care must be exercised in minimizing the influence of these factors on the analysis.
Most commercially available X-ray analytical instruments are designed with inverted optics geometry. The excitation source in this arrangement is located beneath the sample and provides a sample plane which is horizontally positioned above the optics. A liquid and/or loose powdered sample substance is generally gravity supported on a thin film substance attached to the sample cup. In this arrangement, the thin film substance, as mentioned above, defines the sample plane. In order to maintain a statistically reproducible sample plane to excitation source distance, allowances must be made for thin film distortion which is attributed to thermal and pressure differences. The distortion either increases or decreases the distance between the sample plane and the excitation source which results in higher or lower values than would be had without the distortion.
The sample preparation procedure for the above described arrangement, however, is relatively simple as it consists of merely ensuring that the sample cup contains an adequate quantity of sample substance such that the required critical depth of penetration is satisfied.
Other types of instrumentation have configurations and arrangements that require an upright, horizontal, or inclined sample plane. These arrangements generally require more manual dexterity in accommodating a liquid type specimen than do the inverted geometry arrangements described earlier. This increase in manual dexterity is required in order to maintain a reproducible and uniform distance from the sample plane to the excitation source. Thus, the difficulties associated with X-ray systems of this classification are related to convenience which impacts on the ability to statistically reproduce the distance of the sample plane to the excitation source.
The initial introduction of the sample substance to the main cell of the sample cup assembly, the attachment of the thin film to the open end of the main cell and the retention of the sample within the sample cup during the analysis, generally demands a great deal of time and effort on the part of the technician because the sample plane is located at the top of the sample cup assembly. In order to define the sample plane, the sample cup assembly must be completely filled prior to attachment of the thin film substance and particularly to avoid entrapment of air. Furthermore, the thermal and pressure differentials frequently encountered result in the creations of bubble occlusions within the liquid specimen that generally rise and collect at the interface of the thin film substance and sample surface. This condition can potentially create erroneous analytical data.
In upright horizontal sample plane geometries, bubble occlusions tend to randomly disburse at the surface of the liquid specimen and beneath the thin film substance. In contrast, bubble formations which occur with instruments utilizing inclined sample plane geometries, collect and are generally confined to the upper most area of the sample cup assembly. The focal area of X-ray impingement on the sample, however, is generally small enough to allude the effects of the side collected bubble occlusions on the analytical data.
Until now, no prior art sample cup assemblies have been designed to comprehensively resolve all the difficulties associated with analyzing liquid samples in upright, horizontal, or inclined sample plane systems without having to resort to intricate and costly sample cup designs and methods that are generally very time consuming for assembly and for the most part, are not entirely effective. Moreover, prior art liquid cells primarily designed for inverted optics are also used for upright, horizontal, inclined sample plane geometry systems. The design of these sample cup assemblies allows air to remain entrapped at the interface of the liquid sample plane and the thin film sample support material. The present invention addresses the problems associated with prior art sample cup assemblies by providing a sample cup assembly having a main cell with two open ends which must be assembled. Such cups have been used in many different fields of endeavor as can be seen be looking at U.S. Pat. No. 4,046,138 DIAGNOSIS DEVICE FOR LIQUID SAMPLES issued on Sep. 6, 1977 to Gary Lipin et al., U.S. Pat. No. 4,587,857 entitled METHOD FOR MOUNTING POORLY CONSOLIDATED CORE SAMPLES issued on May 13, 1986 to Darrell C. Bush, and U.S. Pat. No. 4,982,615 entitled STERILE CONTAINER FOR COLLECTING BIOLOGICAL SAMPLES FOR PURPOSES OF ANALYSIS issued on Jan. 8, 1991 to Bernard Sultan et al. All of these patents disclose sample holders with a main cell having two open ends which must be assembled, however, none of these sample cup assemblies are designed for use in X-ray spectroscopy. Furthermore, the present invention also provides means for filling the sample cup once the parts of the sample cup assembly have been assembled. Such a feature is not disclosed or suggested in any of the prior art patents described above.
It is, therefore, an object of the present invention to provide an improved sample cup assembly which includes means for conveniently filling the sample cup once it is assembled without entrapping air at the sample liquid/sample support film interface.